1. Field of the Invention
The present invention relates to a coated cemented carbide cutting tool member (hereinafter referred as xe2x80x9ccoated carbide memberxe2x80x9d) that resists breakage and chipping of its cutting edge for a long period of time, particularly when it is applied to cutting operations of extremely severe conditions such as high speed, high feed, thick depth-of-cut interrupted cutting of steels and cast irons.
2. Description of the Related Art
Coated carbide members are widely used in various fields of cutting operations, for example, continuous and interrupted cutting operation of metal work pieces such as steels and cast irons. Coated carbide members are typically manufactured by depositing a hard coating layer having an average thickness of 3 to 25 xcexcm and including (a) at least one titanium compound layer having an average thickness of 0.1 to 5 xcexcm and composed of at least one layer of granular titanium compound selected from titanium carbide (hereinafter referred to as xe2x80x9cTiCxe2x80x9d), titanium nitride (TiN), titanium carbonitride (TiCN), titanium oxide (Ti2O3), titanium carboxide (TiCO), titanium nitroxide (TiNO) and titanium carbonitroxide (TiCNO), (b) TiCN layer having longitudinal growth crystal structure (1-TiCN) with its average thickness of 2 to 15 xcexcm, and (c) aluminum oxide (Al2O3) layer having an average thickness of 0.5 to 8 xcexcm, on tungsten carbide-based cemented carbide substrate. The common technique for depositing hard coating layer includes CVD (Chemical Vapor Deposition) and/or PVD (Physical Vapor Deposition).
Al2O3 has several different crystal polymorphs, among which the alpha-Al2O3 is known as thermodynamically the most stable polymorph having corundum structure, and typical polymorphs of Al2O3 used as a hard coating layer are stable alpha-Al2O3 and meta-stable kappa-Al2O3. 1-TiCN layer is manufactured by the CVD method at moderate temperatures such as 700 to 950xc2x0 using a reaction gas mixture, which includes organic cyanide compounds such as acetonitrile (CH3CN), such as disclosed in Japanese Unexamined Patent Publication No.6-8010 and No.7-328808.
In recent years, there has been an increasing demand for cutting operations that save labor and time. Accordingly, the conditions under which the cutting operation takes place have become more severe, i.e., high speed, high feed and thick depth-of-cut. With regard to conventional coated carbide members, the 1-TiCN layer found in conventional hard coating layers has fairly good toughness itself, and consequently the whole hard coating layer also shows sufficient toughness. Thus, the conventional hard coating layer exhibits excellent cutting performance without any chipping at cutting edge during continuous high speed cutting operations. When subjected to extremely severe cutting conditions (e.g., high speed, high feed and thick depth-of-cut interrupted cutting), however, the cutting edge of conventional hard coating layers are subject to chipping because of insufficient toughness, and, consequently, the tool lifetime becomes shorter.
Accordingly, one object of the present invention is to provide a coated carbide member that resists chipping of cutting edge over long periods of time even when used for high speed, high feed, and thick depth-of-cut interrupted cutting operations of steels and cast irons.
This and other objects have been attained by the present invention, the first embodiment of which provides a coated cemented carbide cutting tool member, which includes:
a substrate and a hard coating layer deposited on the substrate, wherein the hard coating layer has an average thickness of 3 to 25 xcexcm and includes:
(1) at least one layer having an average thickness of 0.1 to 5 xcexcm and including a granular Ti compound selected from the group including TiC, TiN, TiCN, Ti2O3, TiCO, TiNO, TiCNO and mixtures thereof;
(2) a TiCN layer having an average thickness is 2 to 15 xcexcm and including a longitudinal growth crystal structure; and
(3) an Al2O3 layer having an average thickness of 0.5 to 8 xcexcm;
wherein the TiCN layer includes a growth direction and a compositional gradient of carbon and nitrogen along the growth direction.
Another embodiment of the present invention is a process for producing a coated carbide member, which includes:
depositing a TiCN layer with a reactive gas, the layer having a lower portion and an upper portion; and
during the depositing, changing a concentration in the reactive gas of at least one selected from the group including CH3CN, CH4, N2, and mixtures thereof; wherein
the depositing of the lower portion is carried out at a deposition temperature of 850-950xc2x0 C., and the depositing of the upper portion is carried out at a deposition temperature of 960-1040xc2x0 C.
Another embodiment of the invention provides a coated carbide member, produced by the above-noted process.
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description of the preferred embodiments of the invention.
The present invention is particularly suitable for providing a hard coating layer that is coated on the cutting member of a cutting tool. The term xe2x80x9ccutting memberxe2x80x9d refers to the part of the cutting tool that actually cuts the work piece. Cutting members preferably include exchangeable cutting inserts which are mounted on the bit holders of turning tools, face milling cutter bodies, and end-milling cutter bodies. Cutting members also preferably include the cutting blade of drills and end-mills. The cutting member is preferably made of tungsten carbide-based cemented carbide substrates.
The order of depositing the layers (1-3) is not particularly limited, and more than one of each layer may be deposited, so long as at least one of each layer is present.
Preferably, the hard coating layer is deposited on the substrate by chemical vapor deposition and/or physical vapor deposition.
The hard coating layer preferably coats a portion of the surface, more preferably the entire surface of the cutting member. The hard coating layer preferably includes (a) at least one titanium compound layer composed of at least one layer of granular titanium compound selected from TiC, TiN, TiCN, Ti2O3, TiCO, TiNO and TiCNO, (b) 1-TiCN layer having a compositional gradient of C and N along with its growth direction, and expressed as TiC1xe2x88x92xNx, wherein x ranges from 0.45 to 0.95 at top portion, and it ranges from 0.05 to 0.40 at bottom portion, and (c) Al2O3 layer.
Preferably, the growth direction of the (gradient) TiCN layer is from the surface on which the TiCN layer is deposited, and the terms xe2x80x9cupperxe2x80x9d or xe2x80x9ctopxe2x80x9d portion and xe2x80x9clowerxe2x80x9d or xe2x80x9cbottomxe2x80x9d portion are with respect to the surface on which the TiCN layer is deposited; the lower or bottom portions being deposited first, and the upper or top portions being deposited on the lower or bottom portion. The TiCN layer may be preferably deposited on the substrate, or may also preferably be deposited on one or more intervening layers.
The present invention is particularly suitable for coated carbide member having a long lifetime and whose hard coating layer has excellent toughness characteristics. The present inventors have found:
(A) Continuous or periodical changes of the gas concentration of the reactive gas component such as CH3CN, CH4 and/or N2 during the deposition of 1-TiCN layer gives 1-TiCN layer that has a compositional gradient of C and N along with its growth direction, and preferably the concentration of C decreases and that of N increases from bottom to top in that layer. This gradient 1-TiCN layer is preferably expressed by molecular formula TiC1xe2x88x92xNx, wherein x is the atomic ratio of N to the sum of C and N, and it ranges from 0.45 to 0.95 at top portion of the gradient 1-TiCN layer and ranges from 0.05 to 0.40 at bottom portion of it. The concentration gradient from bottom portion to top portion may vary continuously or step by step, owing to its manufacturing gas condition.
Preferably, the deposition temperature is changed from 850-950xc2x0 C. for the bottom portion to 960-1040xc2x0 C. for the top portion together with the change in gas concentration mentioned above, in terms of giving a more favorable crystal structure of the gradient 1-TiCN layer. More preferably, the bottom portion is deposited at a deposition temperature of 875-925xc2x0 C., most preferably 885-900xc2x0 C. More preferably, the top portion is deposited at a deposition temperature of 980-1020xc2x0 C., most preferably 990-1010 C.
(B) The gradient 1-TiCN layer according to the invention has excellent toughness compared to conventional 1-TiCN layer manufactured by CVD method at moderate temperature range such as 700 to 950xc2x0 C. without any compositional gradient. Therefore, in the coated carbide member that includes the gradient 1-TiCN layer according to the present invention as a constituent of hard coating layer, the hard coating layer itself desirably exhibits excellent toughness and imparts excellent long tool lifetimes without any chipping at the cutting edge, even when it is applied to extremely severe cutting operations such as high speed, high feed, and thick depth-of-cut interrupted cutting of steels and cast irons.
The present invention provides for a coated carbide member that exhibits superior resistance against chipping at cutting edge for a long period of time even when it is applied to extremely severe cutting operations such as high speed, high feed, and thick depth-of-cut interrupted cutting of steels and cast irons, because of excellent toughness of the hard coating layer, by providing a coated carbide member preferably composed of a cemented carbide substrate and a hard coating layer preferably having an average thickness of 3 to 25 xcexcm formed on the substrate by means of CVD and/or PVD method, and that comprise (a) at least one titanium compound layer having average thickness of 0.1 to 5 xcexcm and composed of at least one layer of granular titanium compound selected from TiC, TiN, TiCN, Ti2O3, TiCO, TiNO and TiCNO, (b) 1-TiCN layer that has compositional gradient of C and N along its growth direction having average thickness of 2 to 15 xcexcm and expressed by molecular formula TiClxe2x88x92xNx, wherein x is the atomic ratio of N to the sum of C and N, and it ranges from 0.45 to 0.95 at top portion and ranges from 0.05 to 0.40 at bottom portion, and (c) Al2O3 layer having average thickness of 0.5 to 8 xcexcm.
The average thickness of the hard coating layer is preferably 3 to 25 xcexcm, more preferably 5 to 20 xcexcm, and most preferably 7 to 15 xcexcm. Excellent wear resistance cannot be achieved at a thickness of less than 3 xcexcm, whereas breakage and chipping at the cutting edge of the cutting member easily occur at a thickness of over 25 xcexcm.
Individual Ti compound layers are believed to ensure sufficient adherence between different two layers. It becomes difficult to keep sufficient adherence at a thickness of less than 0.1 xcexcm, whereas wear resistance decreases at a thickness of over 5 xcexcm. Accordingly, the average thickness of individual Ti compound layers independently of one another is set to 0.1 to 5 xcexcm, preferably 0.5 to 4.5 xcexcm, more preferably 0.75 to 4 xcexcm, more particularly preferably 1 to 3.5 xcexcm, and most preferably 1.5 to 3 xcexcm.
The Al2O3 layer is believed to increase wear resistance of hard coating layer especially for high speed cutting operation because of its satisfactory properties such as thermal barrier and oxidation resistance. It becomes difficult to achieve enough wear resistance at a thickness of less than 0.5 xcexcm, whereas chipping at cutting edge easily becomes to occur at a thickness of over 8 xcexcm. Accordingly, the average thickness of the Al2O3 layer is set to 0.5 to 8 xcexcm, preferably 0.75 to 74 xcexcm, more preferably 1 to 6 xcexcm, more particularly preferably 2 to 5 xcexcm, and most preferably 3 to 4 xcexcm.
The gradient 1-TiCN layer is believed to improve the toughness of hard coating layer as noted above. It becomes difficult to provide satisfactory properties of this layer at a thickness of less than 2 xcexcm, whereas wear resistance of this layer decrease sharply at a thickness of over 15 xcexcm. Accordingly, the average thickness of the gradient 1-TiCN layer is set to 2 to 15 xcexcm, preferably 2.5 to 12.5 xcexcm, more preferably 3 to 10 xcexcm, more particularly preferably 4 to 7 xcexcm, and most preferably 5 to 6 xcexcm.
With regard to the gradient 1-TiCN layer expressed as TiC1xe2x88x92xNx, when the x value the at top portion is less than 0.45 or when that value at the bottom portion is more than 0.40, the concentration gradient of C and N becomes rather small, and as a consequence further improvement of layer toughness cannot be attained. Similarly, when the x value at the top portion is more than 0.95 or when that value at bottom portion is less than 0.05, it becomes difficult to secure its longitudinal crystal structure, and as a consequence the toughness of the layer decreases sharply, then chipping at the cutting edge may occur. Accordingly, the x value at top portion is preferably set to 0.45 to 0.95, more preferably 0.50 to 0.85, and most preferably 0.55 to 0.75; and the x value at bottom portion is preferably set to 0.05 to 0.40, more preferably 0.10 to 0.35, and most preferably 0.15 to 0.30.
A preferable embodiment is a coated carbide member for a cutting tool that includes a substrate and a hard coating layer on the substrate, wherein the hard coating layer includes (a) at least one titanium compound layer composed of at least one layer of granular titanium compound selected from the group including TiC, TiN, TiCN, Ti2O3, TiCO, TiNO, TiCNO, and mixtures thereof; (b) 1-TiCN layer having a compositional gradient of carbon (C) and nitrogen (N) along with its growth direction (gradient 1-TiCN); and (c) Al2O3 layer,
wherein gradient 1-TiCN is expressed by molecular formula TiC1xe2x88x92xNx, wherein x is the atomic ratio of N to the sum of C and N, and it ranges from 0.45 to 0.95 at top portion of the gradient layer and ranges from 0.05 to 0.40 at bottom portion thereof.
Another preferable embodiment of the present invention is to provide a process for producing a coated carbide member with gradient 1-TiCN layer by changing the gas concentration of the reactive gas concentration of CH3CN, CH4, and/or N2, and the deposition temperature, from 850-950xc2x0 C. for the bottom portion to 960-1040xc2x0 C. for the top portion, during the deposition period of 1-TiCN layer.